Field of the Invention
The invention relates to an x-ray system characterized by having a reduced size such as are found in portable/handheld devices, and in particular, to techniques for manufacturing and using the x-ray system.
Description of the Related Art
There is an interest in compact, low power consumption x-ray devices for a variety of purposes, including portable x-ray analytical instruments capable of providing highly accurate detection capabilities. Providing small form x-ray devices such as portable x-ray fluorescence (XRF) instruments has, however, been a challenge.
For example, the size of conventional high voltage power supplies necessary to power x-ray equipment has constrained designers. This has been exacerbated by associated electrical insulation requirements. x-ray tubes typically used in portable instruments require up to 60,000 Volts accelerating voltage and <1 mA of beam current. The most beneficial arrangement for portable x-ray instrumentation is a grounded anode x-ray source such that a negative high voltage is applied to a cathode end of the x-ray tube, while the output anode end is held at ground potential and presented to the sample. Operation for these types of portable XRF instruments requires independent control of the accelerating voltage and the beam current.
Miniature x-ray tubes with a grounded anode design typically require up to 1 watt of low voltage power applied to a thermionic type filament in order to heat the filament sufficiently to emit electrons. The difficulty is that a relatively high power source is necessary and positioned in close proximity to the x-ray tube which needs to be isolated from ground potential by the full high voltage being applied to the cathode end of the x-ray tube.
Traditional packaging schemes for these miniature high voltage power supplies and x-ray tubes tend to use rigid boards with surface mounted components and a metal enclosure to contain the insulating material, minimize the emitted electrical noise and reduce the chance of corona which can lead to a degradation of the insulating material over time. Because of the proximity of the metal case to the high voltage components of the power supply, space between the components must be filled with materials that comprise a high dielectric breakdown strength. Traditional materials have included transformer oil, dielectric fluids, and polymeric potting materials. These materials usually have a high voltage breakdown strength of 400-800 volts/mil requiring a substantial thickness in order to insulate the high voltage (up to 60,000 volts). For example, a 500 volt/mil material would need a minimum of about 0.120″ and normally a 100% safety margin is used resulting in a 0.240″ requirement in all directions for electrical insulation.
In addition it is generally advantageous to position the x-ray devices within a portable XRF instrument in close proximity to the components that interact with a sample such as the components in the “nose” of a device that direct an x-ray beam to the sample. It is understood that x-ray radiation is a type of “ionizing” radiation that can be harmful to living tissue and thus it is generally appreciated that portable XRF devices are constructed to emit relatively low photon energies that typically attenuate over short distances (e.g. when an x-ray beam travels through air) in order to minimize the risk associated with operating an XRF device. Typically, the region of XRF devices near the nose of the instrument are very space constrained in the interest of making the XRF device easily manageable for a user and capable of fitting into small spaces where a sample resides. An example of an x-ray device constructed for use in a portable XRF instrument is described in U.S. Pat. No. 9,281,156, titled “Volumetrically Efficient Miniature X-Ray System”, which is hereby incorporated by reference herein in its entirety for all purposes.
Therefore it is appreciated that there are significant advantages in having x-ray generators with high voltage multiplier components that comprise a dimension that fits into a region of a portable XRF device that is proximal to a sample to be tested while providing the necessary performance characteristics. For example, the desired solutions result in a versatile, low cost x-ray generator that provides laboratory grade performance in a portable XRF instrument.